Schmidt SS 20.260 User manual

SCHMIDT®Flow Sensor
SS 20.260
Instructions for Use

Instructions for Use SS 20.260 Page 2
SCHMIDT®Flow Sensor
SS 20.260
Table of Contents
1Important information.......................................................................3
2Application range.............................................................................4
3Mounting instructions.......................................................................4
4Electrical connection......................................................................11
5Signalization..................................................................................12
6Startup...........................................................................................14
7Information concerning operation..................................................15
8Service information........................................................................16
9Technical data ...............................................................................17
10 EC Declaration of conformity.........................................................18
Imprint:
Copyright 2011 SCHMIDT Technology GmbH
All rights reserved
Version 508981.02E
Subject to modifications

Instructions for Use SS 20.260 Page 3
1 Important information
The instructions for use contain all required information for a fast com-
missioning and a safe operation of the SCHMIDT®flow sensor
SS 20.260:
These instructions for use must be read completely and observed
carefully, before putting the unit into operation.
Any claims under the manufacturer's liability for damage resulting
from non-observance or non-compliance with these instructions will
become void.
Tampering with the device in any way whatsoever - with the excep-
tion of the designated use and the operations described in these in-
structions for use - will forfeit any warranty and exclude any liability.
The unit is designed exclusively for the use described below (see
chapter 2). In particular, it is not designed for direct or indirect per-
sonal protection.
SCHMIDT Technology cannot give any warranty as to its suitability
for certain purpose and cannot be held liable for accidental or se-
quential damage in connection with the delivery, performance or use
of this unit.
Symbols used in this manual
The symbols used in this manual are explained in the following section.
Danger warnings and safety instructions –read them care-
fully!
Non-observance of these instructions may lead to injury of per-
sonnel or malfunction of the device.
General note
All dimensions are indicated in mm.
!

Instructions for Use SS 20.260 Page 4
2 Application range
The SCHMIDT®flow sensor SS 20.260 is designed for stationary
measurement of the flow velocity as well as the temperature of air and
gases under atmospheric pressure.
The sensor is based on the measuring principle of the thermal anemom-
eter and measures the mass flow of the measuring medium as flow ve-
locity which is output in a linear way as standard velocity
1
wN (unit: m/s),
based on standard conditions of 1013.25 hPa and 20 °C. Thus, the re-
sulting output signal is independent from the pressure and temperature
of the medium to be measured.
The SCHMIDT® flow sensor SS 20.260 is designed for the use inside
closed rooms and is not suitable for outdoor use.
3 Mounting instructions
General information on handling
The SS 20.260 is a precision instrument with high measuring sensitivity.
In spite of the robust construction of the sensor tip soiling of the inner
sensor elements can lead to distortion of measurement results (see also
chapter 8 Service information). During procedures that could stimulate
soiling like transport, mounting or dismounting of the sensor it is recom-
mended to place the enclosed SCHMIDT Technology protective cap on
the sensor tip and remove it only during operation.
During processes with enhanced risks of soiling such as
transport or mounting the protective cap should be placed onto
the sensor tip.
General installation conditions
The sensor measures the flow speed correctly only in the direction given
on the housing and sensor head (arrow). Make sure that the sensor is
adjusted in flow direction; a tilting of up to ±3° is allowed
2
.
The sensor measures unidirectional and must be adjusted cor-
rectly relative to the flow direction.
A sensor mounted in opposite direction of the flow direction leads to
wrong measuring values (too high).
1
Equates to the real flow velocity under standard conditions
2
Measurement deviation < 1 %
!
!

Instructions for Use SS 20.260 Page 5
The lower measuring range limit is according to the system
requirements 0.2 m/s.
At lower flow velocities (< 2 m/s) the measured medium tem-
perature is too high.
The center of the chamber head is the actual measuring point of the flow
measurement and must be placed in the flow as advantageous as possi-
ble, for example in the middle of a pipe (see Figure 1). Therefore this
point is also used for specification of probe length L (see Figure 2).
Figure 1 Positioning in a pipe
In closed systems the sensor head must be located in the cen-
ter of the pipe.
Installation with low disturbance
Local turbulences of the medium can cause distortion of measurement
results. Therefore, appropriate mounting conditions must be guaranteed
to ensure that the gas flow is supplied to the sensor in a quiet and low in
turbulence state in order to maintain the accuracy specified (see chapter
9 Technical data).
Correct measurements require quiet flow, as low-turbulence as
possible.
An undisturbed flow profile can be achieved if a sufficiently long distance
in front of (run-in distance) and behind (run-out distance) the sensor in-
stallation site (see Figure 2) is held absolutely straight and without dis-
turbances (such as edges, seams, bends etc.). It is also necessary to
pay attention to the design of the run-out distance because disturbances
also generate turbulences against the flow direction.
!
!
!
!
Flow
Direction of measurement

Instructions for Use SS 20.260 Page 6
L
= Length of entire measuring distance
L1
= Length of run-in distance
L2
= Length of run-out distance
D
= Inner diameter of measuring distance
Figure 2
The following Table 1 shows the required straight conduit lengths de-
pending on the pipe inner diameter “D” and the different disturbance
causes.
Flow obstacle upstream of the measuring dis-
tance
Minimum
length of L1
Minimum
length of L2
Light bend (< 90°)
10 x D
5 x D
Reduction / expansion / 90° bend or T-junction
15 x D
5 x D
Two 90° bends in one plane (2-dimensional)
20 x D
5 x D
Two 90° bends (3-dimensional change in direction)
35 x D
5 x D
Shut-off valve
45 x D
5 x D
Table 1
This table lists the minimum values required in each case. If the listed
straight conduit lengths cannot be achieved, measurement accuracy
may be impaired
3
.
Calculation of volume flow
If the cross section area of the pipe is known, the output signal of the
flow speed can be used to calculate the standard volumetric flow of the
medium. By means of a correction factor PF
4
, which depends on the
pipe diameter the measured value can be converted to an averaged flow
wNwhich is constant over the whole pipe cross-section.
Thus, it is possible to calculate the standard volumetric flow of the medi-
um using the measured standard flow velocity in a pipe with known inner
diameter:
3
Alternatively flow rectifier could be used, e.g. honeycomb ceramics
4
Considers parabolic flow profile and sensor obstruction

Instructions for Use SS 20.260 Page 7
EFAwV
wPFw
DA
NN
NN




2
4

Table 2 lists profile factors and volume flow measuring ranges (with cer-
tain sensor measuring ranges) for standard pipe diameters.
Table 2
Inner Min. @
DN [inch]
[mm] PF 0,2 m/s 2,5 m/s 20 m/s 50 m/s
25 25 126.0 0.796 0.30 3.80 30.4 76.1
32 32,8 0.796 0.48 6.05 48.4 121
1 1/4 36,3 0.770 0.57 7.17 57.4 143
40 40 1 1/2 39,3 0.748 0.65 8.17 65.3 163
43,1 0.757 0.80 9.94 79.5 199
45,8 0.763 0.91 11.3 90.5 226
50 50 2 51,2 0.772 1.14 14.3 114 286
57,5 0.777 1.45 18.2 145 363
65 65 2 1/2 70,3 0.786 2.20 27.5 220 549
76,1 0.792 2.59 32.4 259 648
80 80 3 82,5 0.797 3.07 38.3 307 767
100 100 4 100,8 0.804 4.62 57.7 462 1.155
125 125 5 125,0 0.812 7.17 89.7 717 1.794
150 150 6 150,0 0.817 10.4 130 1.040 2.599
180 182,5 0.825 15.5 194 1.554 3.885
200 200 8 206,5 0.829 20.0 250 1.999 4.998
250 10 260,4 0.835 32.0 400 3.202 8.004
300 300 12 309,7 0.840 45.6 570 4.556 11.390
350 14 339,6 0.842 54.9 686 5.491 13.728
400 400 16 389 0.845 72.2 903 7.223 18.058
450 450 18 437 0.847 91.5 1.143 9.147 22.867
500 500 20 486 0.850 114 1.419 11.353 28.383
600 600 24 585 0.854 165 2.066 16.527 41.317
700 700 28 684 0.857 227 2.834 22.673 56.683
800 800 32 783 0.859 298 3.723 29.781 74.452
900 900 36 882 0.862 379 4.740 37.920 94.800
1000 1000 40 980 0.864 469 5.865 46.923 117.308
Nominal
size
Diameter of measuring pipe
Profile
faktor
Measuring range of volumetric flow [m3/h]
Norm value
@ sensor measuring range [m/s]
D
Inner diameter of pipe [m]
A
Cross-section area of pipe [m2]
N
w
Flow velocity in the middle of the pipe [m/s]
N
w
Average flow velocity in the pipe [m/s]
PF
Profile factor (for pipes with circular cross-sections)
EF
Measuring unit factor (conversion to non-SI units)
N
V

Standard volumetric flow [m³/s]

Instructions for Use SS 20.260 Page 8
The measuring unit factor EF serves only for convenient conversion to
non-SI measuring units, for example m3/h (see Table 3).
Measuring unit of diameter D
EF
m
cm
mm
Measuring unit
volumetric flow
m3/s
1
1,0E-04
1,0E-06
m3/min
60
6,0E-03
6,0E-05
m3/h
3600
3,6E-01
3,6E-03
l/s
1000
1,0E-01
1,0E-03
l/min
6,0E+04
6
0,06
l/h
3,6E+06
360
3,6
Table 3
SCHMIDT Technology provides a convenient calculation tool to com-
pute flow velocity or volume flow in pipes for all its sensor types and
measuring ranges. This “Flow Calculator” can be directly used on or
downloaded from SCHMIDT homepage:
http://www.schmidttechnology.de/de/sensorik/download/FlowCalculator.zip
Mounting in a wall
The housing has an external thread M18 x 1 (19 mm long) for direct
mounting on or in the medium separating wall. Its advantage is in the
simplicity of installation without special accessories; however, the im-
mersion depth is defined by the probe length in this case and requires
access from both sides for operation.
Drill a bore in the wall with 13 … 14 mm diameter.
Carefully insert measuring probe with an attached protection sleeve
into the bore so that the mounting block of the enclosure is in contact
with the wall.
Screw on the enclosed fastening nut by hand on the medium side,
turn sensor into required position and tighten fastening nut (SW22)
while holding up the enclosure on the mounting block by means of
SW30.
Angular deviation should not be greater than 3° relative to
ideal position.
Check the set angular position carefully, for example by means of a
spirit level at the hexagonal part of the sensor enclosure.
Finally, remove protective cap from sensor tip.
!

Instructions for Use SS 20.260 Page 9
Mounting with a compression fitting
The sensor is installed using a special compression fitting. Normally, a
sleeve is welded as a connecting piece onto a bore in the medium-
guiding pipe, in which the external thread (G½) of the compression fitting
is screwed (see Figure 3).
Figure 3
L
Probe length [mm]
SL
Length of weld-in sleeve [mm]
AL
Projecting length [mm]
DA
Outer diameter of pipe [mm]
MID
Minimum immersion depth [mm]
E
Setting length of probe [mm]
Bore a mounting opening in a pipe wall.
Weld connecting piece with an internal thread G½ in the center
above the mounting opening on the pipe.
Recommended length of connecting piece: 15 ... 40 mm
If necessary wrap thread using a common sealing tape, for example
made of PTFE.
Screw threaded part of compression fitting one or two turns by hand
into connecting piece then tighten it with a screw wrench (SW27).
Remove compression fitting nut and extract both poetry halves.
Remove protective cap from sensor tip and attach compression fit-
ting nut on sensor probe.
Insert probe in threaded part of the compression fitting, attach poetry
halves and screw on fitting nut manually to such an extent that sen-
sor probe can be inserted without jamming.
L
AL
66SL 32
MET=20
8 E
D
A
MID = 20

Instructions for Use SS 20.260 Page 10
In case of a longer sensor probe push it partly into the pipe as re-
quired.
Always avoid bending of the probe during screwing.
Carefully slide probe so that the center of the chamber head is
placed at the optimum measuring position in the middle of the pipe.
Tighten compression fitting nut slightly by hand so that sensor is
fixed.
Turn sensor manually at its enclosure into required direction and
precise position while maintaining immersion depth.
Angular deviation should not be greater than 3° relative to
ideal position.
Hold sensor and tighten compression fitting nut by turning the fork
wrench (SW17) a quarter of a turn.
Recommended torque: 10 … 15 Nm
Check the set angular position carefully, for example by means of a
spirit level at the hexagonal part of the sensor enclosure.
Mounting accessories
Type / article No.
Drawing
Mounting
Clamp5
a.) 524 916
b.) 524 882
- Internal thread G½
- Material:
a.) Steel, black
b.) Stainless steel 1.4571
Compression fitting
Brass
517 206
51 12
1/2G
SW24
SW27
9
- Immersion sensor
- Pipe (typ.), wall
- Screwing into a welding
stud
- Material:
Brass
PTFE, NBR
Atmospheric pressure use!
Table 4
5
Must be welded
!
!
26,6
34
Rp1/2

Instructions for Use SS 20.260 Page 11
4 Electrical connection
During electrical installation ensure that no voltage is applied
and inadvertent activation is not possible.
The sensor is electrically connected according to Table 5 by means of
the open cable ends of a 4-wire cable firmly fixed to the sensor housing.
Wire color
Designation
Function
Brown (BR)
Power
Operating voltage: +UB
White (WH)
GND
Operating voltage: Mass
Yellow (YE)
Analog wN
Output signal: Flow velocity
Green (GR)
Analog TM
or
AGND
Output signal: Temperature of the medium
or
Ground connection of analog output
Table 5
Operating voltage
For proper operation the sensor requires DC voltage with a nominal val-
ue of 24 V with permitted tolerance of ±10 % and the sensor is protected
against a polarity reversal.
Deviating values lead to deactivation of the measuring function or even
to failure. As far as it is possible, the LED indication as well as both ana-
log outputs report faulty operational conditions (see chapter 5Signaliza-
tion).
Only operate sensor within the defined range of operating volt-
age (24 V DC ± 10 %). Undervoltage may result in malfunction.
Overvoltage may lead to irreversible damage to the sensor.
Wiring of analog outputs
The analog output of the basic variant of the sensor (“-1”), which
measures only flow velocity, is alternatively (order option) of the type
tension (0 … 10 V)
6
or laid-out as current interface (4 … 20 mA). The
enhanced version (“-2”) with an additional analog output for signalizing
the temperature of the medium comes with 2 current interfaces. Either
type of analog outputs exhibits permanent short-circuit protection against
both rails of the operating voltage UB.
6
It is recommended, to use AGND as measuring reference potential for tension output.
!
!

Instructions for Use SS 20.260 Page 12
Voltage output (wN)
Current interface (wN,TM)
UA= 0 ... 10 V RL≥10 k
IA= 4 ... 20 mA RL≤300 
Figure 4
The apparent ohmic resistance RLmust be connected between the sig-
nal output and GND (see Figure 4). Load capacity CLis limited to a max-
imum of 10 nF.
5 Signalization
Light emitting diodes
The sensor is equipped with 2 light emitting diodes (LED) indicating its
functional state.
Figure 5
Operating state
LED 1
LED 2
Supply voltage too low
Ready for operation
Supply voltage too high
Medium temperature beyond specification range
Sensor defective
Table 6
LED off
LED flashes (approx. 2 Hz): green
LED on: green
LED flashes (approx. 2 Hz): red
LED 1
LED 2
Flow

Instructions for Use SS 20.260 Page 13
Analog outputs
Error signaling
If the supply voltage is too high or if the sensor detects a defect, one
respectively both interfaces emit 0 V or 2 mA
7
.
Representation of the measuring range
The measuring range of the corresponding measuring value is
mapped in a linear way to the signaling range of its analog output.
For flow measurement the measuring range reaches from zero to the
selectable end of the measuring range wN,max (= 100 % in Figure 6).
A higher flow up to 110 % (= 11 V or 21.6 mA) is still output in a line-
ar way, moreover the signal remains constant.
Voltage output wN
Current interface wN
wNOut
N
NU
V
w
w,
max,
10 
)4(
16 ,
max, mAI
mA
w
wwNOut
N
N
Figure 6 Representation for flow velocity
The measuring range of the medium temperature is -20 to +120 °C
(Figure 7). Falling below this temperature it is still output in a linear
way down to -30 °C (3 mA), going deeper the signal remains con-
stant. An exceeded of the temperature range is output in a linear
way up to +130 °C (21.2 mA), moreover this output remains con-
stant.
For a correct temperature measurement, the flow velocity
on the sensor head must be > 2 m/s. An excessive tem-
perature value is output if flow velocity is < 2 m/s.
7
In accordance with NAMUR specification
!

Instructions for Use SS 20.260 Page 14
Current interface TM
CmAI
mA
C
TwNOutM 

20)4(
16
140 ,
Figure 7 Representation for medium temperature
Even short-term overshooting of the operating medium
temperature can cause irreversible damage of the sensor.
6 Startup
Prior to switching on the SCHMIDT®flow sensor SS 20.260, the follow-
ing checks have to be carried out:
Immersion depth of the sensor probe and alignment of the housing
Tightening of the fastening screw of the compression fitting
Correct electrical connection in the field (switch cabinet or similar)
Prior to startup the sensor check mounting and electrical
connection.
5 seconds after switch-on the sensor is ready for operation. If the sensor
has another temperature than the ambient, this time is prolonged until
the sensor has reached its ambient temperature.
If the sensor has been stored at very cold conditions, before commis-
sioning you have to wait until the sensor and its housing have reached
ambient temperature.
!
!

Instructions for Use SS 20.260 Page 15
7 Information concerning operation
Soiling or other gratings on the sensor cause distortions of
measurements.
Therefore, the sensor must be checked for soiling at regular
intervals and cleaned if necessary.
(Condensating) liquid on the sensor causes serious measure-
ment distortions.
After drying the correct measuring function is restored.
Eliminating malfunctions
The following Table 7 lists possible errors (error images). A description
of the way to detect errors is given. Furthermore, the possible causes
and measures to be taken to eliminate errors are listed.
Error image
Possible causes
Troubleshooting
Problems with supply voltage UB:
No UBavailable
UBhas wrong polarity
UB< 15 V
Sensor defective
Sensor cable connected cor-
rectly?
Supply voltage connected to
the control?
Supply cable broken?
Power supply unit large
enough?
IwN , ITM = 0 mA
Sensor element defective
Send in sensor for repair
IwN , ITM = 2 mA
Operating voltage too high
Check the operating voltage and
reduce it
IwN , ITM = 2 mA
Flow signal wNis
too large / small
Measuring range too small /large
Medium is not air
Sensor element soiled
Sensor installed in opposite direc-
tion to flow direction
Check sensor configuration
Check measuring resistance
Is the foreign gas factor correct?
Clean sensor tip
Check the installation direction
Flow signal wNis
fluctuating
UBunstable
Mounting conditions:
Sensor head is not in optimal
position
Run-in/run-out distance is too
short
Strong fluctuations of pressure or
temperature
Check the voltage supply
Check mounting conditions
Check operating parameters
Table 7
!
!

Instructions for Use SS 20.260 Page 16
8 Service information
Maintenance
Soiling of the sensor element may lead to a wrong measuring result. The
sensor tip must be checked regularly for soiling and must be cleaned
when required.
Cleaning of the sensor tip
The sensor tip can be cleaned to remove dust or soiling by moving it
carefully in warm water containing a washing-up liquid. If necessary a
soft brush can be used additionally.
Do not use strong cleaners, solvents, brush or other hard ob-
jects.
Before putting it again into operation, wait until the sensor tip is com-
pletely dry.
Transport / shipment of the sensor
Before transport or shipment of the sensor, the delivered protective cap
must be placed onto the sensor tip. Avoid soiling or mechanical stress.
Recalibration
If the customer has made no other provisions, we recommend repeating
the calibration at a 12-month interval. To do so, the sensor must be sent
in to the manufacturer.
Spare parts or repair
No spare parts are available, since a repair is only possible at the manu-
facturer's facilities. In case of defects the sensors must be sent in to the
producer for repair.
If the sensor is used in systems important for operation, we recommend
you to keep a replacement sensor in stock.
Test certificates and material certificates
Every new sensor is accompanied by a certificate of compliance accord-
ing to EN10204-2.1. Material certificates are not available.
Upon request, we shall prepare, at a charge, a factory calibration certifi-
cate, traceable to national standards.
!

Instructions for Use SS 20.260 Page 17
9 Technical data
Measuring parameters
Standard velocity wNof air, based on standard conditions 20 °C
and 1013.25 hPa
Medium temperature TM
Medium to be measured
Air or nitrogen, other gases on request
Measuring range wN
0 ... 2.5 / 10 / 20 / 40 / 50 m/s
Lower detection limit wN
0.2 m/s
Measuring accuracy wN
- Standard
- Precision*
±(5 % of measured value + [0.4 % of final value; min. 0.02 m/s])
±(3 % of measured value + [0.4 % of final value; min. 0.02 m/s])
Reproducibility wN
±1,5 % of measured value
Response time (t90 ) wN
3s (jump from 5 to 0 m/s)
Temperature gradient wN
< 8 K/min (@ 5 m/s)
Measuring range TM
-20 ... +120 °C
Measuring accuracy TM
(wN≥ 2 m/s)
±1 K (0 ... 40 °C)
±2 K (remaining measuring range)
Operating temperature
- Medium
- Electronics
-20 ... +120 °C
0 ... +70 °C
Humidity range
0 ... 95 % rel. humidity (RH), non-condensing
Operating pressure
atmospheric (700 ... 1300 mbar)
Operating voltage UB
24 VDC ± 10 % (reverse voltage protected)
Mounting tolerance
±3° (relative to flow direction)
Current consumption
< 60 mA
Analog outputs
- Type voltage (U)
- Typ current (I)
- Load capacity
1 or 2 (short-circuit protected)
0 ... 10 V (RL≥ 10 k)
4 ... 20 mA** (RL≤ 300 )
CL≤ 10 nF
Electrical connection
Cable fixed on housing, 4-pin, length 2 m, pigtail***
Line length
≤ 15 m (U) / 100 m (I)
Protection class
III (PELV)**** according EN 50178)
Type of protection
IP 65
Mounting
Thread M18 x 1 at sensor enclosure, accessories (option)
Installation length
50 / 100/ 200 / 350 / 500 mm
Weight
200 g max.
Table 8
*Under alignment conditions and with regard to the reproducibility of the reference
** Error messaging: 2 mA; exceeding measuring range: up to 22 mA
*** With cable end sleeves
**** According EN 50178

Instructions for Use SS 20.260 Page 18
10 EC Declaration of conformity

Instructions for Use SS 20.260 Page 19
Notes:

Instructions for Use SS 20.260 Page 20
SCHMIDT Technology GmbH
Feldbergstrasse 1
78112 St. Georgen / Germany
Phone [phone] / 899-0
Fax [phone] / 899-101
[e-mail]
www.schmidttechnology.de